1. Field of the Invention
The present invention relates to cooking, roasting, baking, and grilling devices, as well as parts of these devices, in particular of ovens and stoves which are soiled with remnants of foodstuffs while in use. More specifically, the invention relates to such devices having their surface treated in such a way that such soiling can be better thwarted, and the surface of the device or of a part of the device appears clean even without mechanical cleaning.
2. Discussion of the Related Art
Self-cleaning stove coatings are already known from the state of the art. The first publication of a German patent application DE-A 28 28 613 describes a self-cleaning coating of articles that are heated while in use. The coating comprises a porous layer of a matrix of an inorganic binding agent with a matting agent on the surface of the articles. In this layer are distributed particles of a catalyst (which tends to change its color as a result of its catalytic action), and a non-discoloring substance. The catalytic action is provided by at least one of the metal oxides Mn2O3, MnO2, or CuO and/or by a solid acid catalyst, e.g. zeolite. A suitable group of non-discoloring substances are ferrites. As matting agents are proposed e.g. Al2O3, SiO2, TiO2, ZrO2, ZnO, CaO, or MgO. The mentioned inorganic binding agents include frits of borosilicate glass, phosphate and lead frits and alkaline metal silicates.
Another self-cleaning coating is described in DE-A 29 28 895. On the article that is supposed to be self-cleaning, there is a coating film generated from a mass which comprises an oxidation catalyst, a synthetic silicone resin as binder, and an organic solvent (LM). The coating film is formed by heating of the mass to 300 to 400° C. The catalyst is preferably a precious metal, or a metal oxide or a mixture of two or more metal oxides, in particular Pt, Pd, or MnO2, a Cu-oxide, a Fe-oxide, a Ni-oxide, or a Cr-oxide.
A coating for the fabrication of self-cleaning surfaces comprising an inorganic polymerization inhibitor is described in the printed specification of German patent DE-C 30 19 828. The coating mass required for the production of the coating is dispersed in a liquid binding agent that comprises an oxidation catalyst (metal or metal oxide) as well as the mentioned polymerization inhibitor. Liquid binding agents used include in particular silicone resins dissolved in organic solvents. Polymerization inhibitors used include in particular Al(OH)3, Sb2O3, phosphate frit material or a mixture of at least two of these. The metal oxides/metals are oxides of V, Cr, Mo, Mn, Ni, and Cu, especially MnO2, Ni2O3, CuO, or Pt and Pd, and especially colloidal Pt or Pd on Al2O3.
A coating that prevents or reduces unpleasant odors and surface soils is described in DE-A 199 15 378. The coating mass required for the production of the coating comprises (1) a polycondensate of (a) a silane or an oligomer derived thereof and (b) as necessary, a compound of glass-forming elements as well as (2) particles of a transition metal oxide with a diameter of 10 nm to 20 μm. The silane is a compound of the general formula RaSiX(4-a) with a=0, 1, 2, 3, or 4, wherein R is a non-hydrolyzable radical, X is, in contrast, a hydrolysable radical. Examples of transition metal oxides are the oxides of La, Ce, Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag, or Zn. During the production of the polycondensate or coating mass or thereafter, inorganic particles of nanometer or micrometer scale dimensions, mainly in form of a sol, may be added to the coating mass. Preferred inorganic particles are Al2O3, SiO2, SnO2, iron oxides, and C (graphite, carbon black). The proportions in size for the nanoscale particles are such that the particle size (diameter) is up to 300 nm. However, preferred particle sizes are up to 50 or up to 100 nm.
In the case of micrometer scale particles, a structuring of the coating and the generation of hollow spaces is caused. The particle diameter is 1 to 500 μm in this case. With these particles, Al2O3 and SiO2 are also preferred, in particular kieselguhr, aluminum oxide 90, silica gel 40 or 60.
When these inorganic particles are used, they are impregnated with the transition metal oxide which leads to a decrease in the pore volume of the particles. In the described impregnation by means of salt solution, the inner and outer surfaces are coated which is advantageous for the reduction of unpleasant odors due to the large catalytically active surface (since gases, in contrast to oily substances, can also enter into small pores). This does not apply, though, to the prevention/removal of soils.
These alternatives for self-cleaning coatings that are described to date and are commercially available. They are all characterized by the fact that their self-cleaning ability noticeably decreases relatively fast overtime. Hence, there is a need for better and longer lasting self-cleaning ability possessing coatings in or on cooking, roasting, baking, and grilling devices or their parts, and in particular in ovens and stoves. The quality and durability of the coatings/layers possessing self-cleaning ability of cooking, roasting, baking, and grilling devices may be determined according to DIN ISO 8291 in case of a layer thickness of at least 150 μm. The coatings known in the state of the art can withstand 5-10 cycles of soy bean oil dripping on them and subsequent heating to 250±10° C., before a pigmenting of the surface (assessment according to DIN ISO 8291 through appearance of gloss) occurs. To increase the number of cycles under the defined conditions is consequently the fundamental goal which the inventors of the present invention set out to reach.
The inventors of the present invention have looked for an alternative to this technically unsatisfying situation and confronted themselves with the problem of providing the possibility of changing the treatment of parts in or on cooking, roasting, baking, and grilling devices, in particular ovens and stoves, that with use are often soiled with remnants of foodstuffs, compared to the state of the art in such a way that at least 10-15 cycles according to DIN ISO 8291 are and remain self-cleaning, meaning the soiling by remnants of foodstuffs that occurs during cooking, roasting, backing, and grilling in a e.g. oven/stove on the inner surfaces of the muffles is avoided over a longer period of time (with equal or equally frequent use) without mechanical action and the baking oven muffle looks cleaner than is the case today with conventional coatings.